The present invention relates to an electronic heat pump device for transporting heat from a low temperature section to a high temperature section through, for example, application of a current. The present invention also relates to a laser component for cooling a semiconductor laser diode device by using the electronic heat pump device, an optical pickup equipped with the laser component, and electronic equipment equipped with the electronic heat pump device.
In recent years, images and data recorded by writable optical disk apparatuses are rapidly expanding, by which recording rates as well as optical output from the writable semiconductor laser diodes are steadily increasing.
The semiconductor laser diode device emits light while generating heat whose energy is several times larger than that of the light, and therefore it is concerned that the heat generated by the semiconductor laser diode itself might cause fluctuation in wavelengths and decrease in life.
As an apparatus for cooling the semiconductor laser diode device, a semiconductor laser module equipped with an electronic heat pump device composed of a peltiert device module has conventionally been proposed.
The semiconductor laser module (first prior art example) is composed of, as shown in FIG. 18, a semiconductor laser diode chip (hereinbelow referred to as an LD chip) 101, a metal substrate 104 for mounting a lens, and a peltiert device 105 (see JP 10-200208 A).
The metal substrate 104 is bonded to the top portion of the peltiert device 105 through metal soldering, and for keeping the temperature of the LD chip 101 constant, a thermister 108 is mounted thereon.
Heat travels from the LD chip 101 to the upper surface of the peltiert device 105. Through application of current to the peltiert device 105, the heat moves from the upper surface of the peltiert device 105 to the lower surface, and through control over the current of the peltiert device 105 by an unshown temperature regulation circuit, it becomes possible to keep the temperature of the LD chip 101 constant.
Moreover, as an electronic heat pump device, an apparatus of vacuum diode-type structure different in structure from the peltiert device 105 has been proposed.
The apparatus of vacuum diode-type structure (second prior art), as shown in FIG. 19, functions as an electronic heat pump device in which an emitter electrode 111 and a collector electrode 112 face each other with a vacuum gap 113 interposed therebetween, and a voltage applied to a piezo device 114 for regulating the space between the emitter electrode 111 and the collector electrode 112 is feedback controlled by monitoring its electrostatic capacity so that the voltage is applied in such a way that electrons discharged from the emitter electrode 111 move to the collector electrode 112, thereby achieving transportation of heat drawn from an endoergic section 115 to an exoergic section 116 (see International Publication No. WO 99/13562).
Moreover, as another apparatus of vacuum diode-type structure (third prior art example), there is, as shown in FIG. 20, a thermionic generator of vacuum gap structure having an electron cooling function in which an emitter electrode 111 and a collector electrode 112 are supported by minute barriers 119 (see JP 2002-540636 A).
This apparatus is an apparatus utilizing a phenomenon in which when electrons are injected from the emitter electrode 111 to the barrier 119 and move from the barrier 119 to the collector electrode 112, the electrons are filtered by the barrier 119, and thereby heat moves together with the electrons.
However, the first to third prior art examples had following problems.
In the first prior art example, cooling efficiency of the peltiert device is low, and therefore energy several times larger than that the heat value generated from the semiconductor laser diode must be provided to gain sufficient cooling efficiency.
This is because, as shown in FIG. 21, the peltiert device is structured such that a first metal electrode 121a, a p-type semiconductor 106, a second metal electrode 121b, an n-type semiconductor 107 and a third metal electrode 121c are electrically connected in this sequence in series, and utilizes Peltier effect in which when a voltage is applied from the outside so as to move electrons from the p-type semiconductor 106 to the n-type semiconductor 107, heat generation occurs on the junctions through which electrons move from the first metal electrode 121a to the p-type semiconductor 106, and from the n-type semiconductor 107 to the third metal electrode 121c, whereas heat absorption occurs on the junctions through which electrons move from the p-type semiconductor 106 to the second metal electrode 121b, and from the second metal electrode 121b to the n-type semiconductor 107, resulting in generation of temperature difference between both the ends of the p-type semiconductor 106 and the n-type semiconductor 107. However, inside the p-type semiconductor 106 and the n-type semiconductor 107, there is heat current due to thermal conduction as shown by an arrow 122, which causes a problem of low cooling efficiency and large power consumption.
In the second prior art example, as shown in FIG. 22, electrons emitted from the emitter electrode 111 move to the collector electrode 112 while carrying heat, by which heat is transported by electrons. Since heat transfer from the collector electrode 112 to the emitter electrode 111 is blocked by the vacuum gap 113, one-way flow of the heat current shown by an arrow 123 is achieved, resulting in high cooling efficiency and small power consumption.
However, in this second prior art example, in order to maintain the vacuum gap 113 of 10 nm or less, the piezo device 114 shown in FIG. 19 as well as an electrostatic capacity controller 117 for feedback control of the vacuum gap 113 are required, which causes a problem that the apparatus becomes big and thereby reduction in size and weight is hindered.
Moreover, in the third prior art example, electrons transport heat from the emitter electrode 111 to the collector electrode 112 as shown in FIG. 22. However, as shown in FIG. 20, heat flows through the barrier 119 interposed in between the emitter electrode 111 and the collector electrode 112 due to thermal conduction, which causes a serious problem of poor cooling efficiency and large power consumption because of the same reason as the peltiert device.